In recent years, there has been developed a femoral-to-femoral cardiopulmonary bypass system wherein it is not necessary to open the patient's chest. Such a system has many obvious advantages and is useful in situations where medical treatment can be administered to the heart without having open-chest surgery. To accomplish this, it is necessary to employ large diameter cannulas and catheters in order to maximize blood flow. It is also, of course, important that the necessary connections to the cannulas be made with a minimum of blood loss, in a minimum of time, and with a minimum of trauma and risk to the patient. Cannulating a femoral artery is particularly difficult because of the pressure involved as well as the large flow through the artery. Accordingly, there is a need for improvements in such devices.